Detailed explanation of the composition and performance of lithium battery electrolyte

Lithium battery electrolyte is composed of solvent and solute. Solvents commonly used in lithium battery electrolyte are dimethylformamide, y-butyrolactone, ethylene glycol, glycerol, water and so on. Dimethylformamide is a solvent for military lithium battery capacitors, which has a wide operating temperature range. In Asia, the use of y-butyrolactone as a solvent for electrolytes is also very popular. It is mainly used in low-voltage small capacitors. Capacitors using this solvent as the main solvent have lower ESR. Ethylene glycol is the most widely used solvent, and low-voltage capacitors usually use a system of ethylene glycol plus some water as the solvent. The solutes in the electrolyte are mainly boric acid, borate, carboxylate and a small amount of other inorganic salts, depolarizing hydrogen eliminators, corrosion inhibitors, hydrolysis inhibitors, etc. Regarding the low-pressure electrolyte, a part of water is added artificially to improve the conductivity of the electrolyte; the medium-high-pressure electrolyte usually uses anhydrous glycol system, even if it contains water, it is required to be below 3%. Selection of electrolyte materials for lithium batteries Working electrolyte is one of the key processes for capacitors. As the actual cathode of the capacitor, it is required to have excellent electrochemical characteristics, continuous supply of oxygen ions, and repair of damaged oxide films; it also has to have the best stability, and does not react with the constituent materials or cause corrosion. The working electrolyte is composed of three parts: solvent, solute and additives. 1. The choice of solvent The solvent determines the application range of the capacitor. The solvent is required to have high boiling point, low freezing point, low vapor pressure and viscosity, good solubility for the solute, and meet the electrical performance requirements of the capacitor in the range of -40~+105℃ , Some requirements are 125 ℃ or even 150 ℃ or more (such as energy-saving lamp aluminum electrolytic capacitors), currently commonly used main solvent is ethylene glycol, boiling point is 196 ℃, freezing point is -12 ℃, other auxiliary solvents are: DMF, y- Butyrolactone, diethylene glycol, glycerol, etc. DMF and y-butyrolactone have good low temperature characteristics and are often used in ultra-low temperature electrolytes such as -55°C and other products. 2. The selection of solute. Solute is an important component that supplies positive and negative ions or ionic groups for repairing the oxide film and maintaining the normal operation of the capacitor. Low pressure: ammonium formate, ammonium adipate, ammonium maleate, etc. as solutes; medium and high pressure: ammonium azelate, ammonium sebacate, ammonium adipate, ammonium dodecanoate, ammonium benzoate, and branched Ammonium salt is used as its main solute to ensure high and low temperature characteristics, supply oxidation efficiency and high temperature stability. 3. Selection of additives Additives are used to adjust electrolyte viscosity, conductivity, increase flashover voltage, passivate oxide film, and inhibit hydrogen. Adding phosphoric acid and its salts, nitro compounds, hydrolysis inhibitors, etc. to the electrolyte can significantly improve the characteristics of the electrolyte. Electrolyte testing: There are three important parameters for electrolyte testing: conductivity, pH value, flashover voltage, etc. If necessary, C1-, SO42-, Fe3+, Cu2+, and electrolyte viscosity should also be tested. PH value: generally distributed between 5.5-9.0, mainly due to the characteristics of aluminum and alumina, can be measured with a pH meter. Conductivity: generally distributed between 400uS/cm~80000uS/cm. It can be measured by a conductivity meter. It has a great relationship with product loss and equivalent series resistance. Flash voltage: generally distributed in 100-600V, measured with aluminum foil oxide film withstand voltage detector, electrolyte flash voltage is a key parameter, especially It is a high-voltage electrolyte, and the flash voltage is one of the breakthrough directions of manufacturing technology. The measurement method and material of the flash fire voltage are different for different companies: the external measurement current must be 10mA, 20mA, etc., while our company generally uses 1mA. The materials used for measurement include: high-voltage formed foil (voltage is generally above 590VF), Plain foil, anode foil strip, etc., the measurement area used is also different. The measurement temperature is generally room temperature. It is relatively accurate at 30°C, especially the conductivity, which is greatly affected by temperature. Therefore, the loss of capacitance at different temperatures is also quite distinct, and the pH and flash voltage will also change slightly with temperature. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous article: What are the common problems of lithium batteries? What to do